Should Time Machine created in Mac OS Extended be converted to APFS?

steve626 wrote:

If the disk is a Mac OS Extended format disk that contains an existing Time Machine backup, you aren’t asked to erase and reformat the disk."

Correct. As I said, Big Sur automatically converts it. It doesn't ask. At least that's what it did with my five Macs running Big Sur. 😎

p.s. Specifically, APFS (case-sensitive).

Note that Time Machine disks for Catalina cannot be APFS, they need to be HFS+.

Time Machine disks under Big Sur can be HFS+ or APFS, Apple says APFS is "preferred" for Time Machine under Big Sur.

https://support.apple.com/en-my/guide/mac-help/mh15139/10.15/mac/10.15

dialabrain wrote:

FWIW, Big Sur actually converts Time Machine backups to APFS. Hence, it's not necessary to manually do so.

https://discussions.apple.com/content/attachment/f33ca747-5161-4206-a421-a2e2282b8af2

https://support.apple.com/en-my/guide/mac-help/mh15139/11.0/mac/11.0

[Big Sur section of Apple Instructions, link provided above]

"APFS or APFS Encrypted disks are the preferred format for a Time Machine backup disk. If you select a new backup disk that’s not already formatted as an APFS disk, you get the option to erase and reformat it. If the disk is a Mac OS Extended format disk that contains an existing Time Machine backup, you aren’t asked to erase and reformat the disk."

FWIW, Big Sur actually converts Time Machine backups to APFS. Hence, it's not necessary to manually do so.

It's not necessary.

I forgot to mention, Steve is correct in that Big Sur is the first and only version of macOS that supports Time Machine on APFS formatted drives.